Re: [PATCH 1/1] clocksource: hyper-v: Rework clocksource and sched clock setup

[Daniel Lezcano]

On 19/06/2023 18:44, Michael Kelley (LINUX) wrote:
> From: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> Sent: Monday, June 19, 2023 9:16 AM
> > On 09/06/2023 17:47, Michael Kelley wrote:
> > > Current code assigns either the Hyper-V TSC page or MSR-based ref counter
> > > as the sched clock. This may be sub-optimal in two cases. First, if there
> > > is hardware support to ensure consistent TSC frequency across live
> > > migrations and Hyper-V is using that support, the raw TSC is a faster
> > > source of time than the Hyper-V TSC page.  Second, the MSR-based ref
> > > counter is relatively slow because reads require a trap to the hypervisor.
> > > As such, it should never be used as the sched clock. The native sched
> > > clock based on the raw TSC or jiffies is much better.
> > >
> > > Rework the sched clock setup so it is set to the TSC page only if
> > > Hyper-V indicates that the TSC may have inconsistent frequency across
> > > live migrations. Also, remove the code that sets the sched clock to
> > > the MSR-based ref counter. In the cases where it is not set, the sched
> > > clock will then be the native sched clock.
> > >
> > > As part of the rework, always enable both the TSC page clocksource and
> > > the MSR-based ref counter clocksource. Set the ratings so the TSC page
> > > clocksource is preferred. While the MSR-based ref counter clocksource
> > > is unlikely to ever be the default, having it available for manual
> > > selection is convenient for development purposes.
> > >
> > > Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> >
> > The patch does not apply, does it depend on another patch?
>
> It should apply to linux-next.  It depends on two previous patches from
> Peter Zijlstra in the sched/core branch of tip.  See:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=sched/core&id=9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc
>
> and
>
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=sched/core&id=e39acc37db34f6688e2c16e958fb1d662c422c81

Yeah, but the branch is tip/timers/core

Could you respin against it ?

Thanks

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